Body morphometrics, swimming diversity and niche in demersal sharks: a comparative case study from the Mediterranean Sea

Abstract

SUmmarY: Seven demersal shark species belonging to six families, obtained from the southern mediterranean Sea, were selected as representative of different putative swimming modes, inhabited depths and trophic levels. caudal fin morphometrics (caudal fin span, area and aspect ratio), hepatosomatic index and muscular-skeletal amount per unit length were estimated and compared within and among species by means of both parametric and non-parametric multivariate and univariate statistical procedures. intra-specific variation was related to size and, for one species only, also to sex. two inter-specific patterns of variation were observed: the first pattern was interpreted as a swimming ability gradient between slow benthic and more pelagic species, as a function of caudal morphometry and body characteristics; the second pattern is related to the depth the species inhabit and/or their trophic level. these two hypotheses were tested with the current data and literature information, and discussed in the context of shark swimming modes, habit and environment. based on observed differences in caudal fin morphometrics, liver and muscular masses, this paper is the first to provide a quantitative and comparative dataset for demersal sharks as a group, and attempts to describe sample variability as a function of expected swimming ability and occupied niche (depth inhabited and/or trophic level).Keywords: demersal sharks, swimming ability, tail aspect ratio, hepatosomatic index. reSUmen: Morfometría corporal, diversidad natatoria y nicho de los tiburones demersales: estudio comparativo en el mar Mediterráneo. -Siete especies de tiburones demersales, pertenecientes a 6 familias, capturadas en el sur del mar mediterráneo, fueron seleccionadas como representantes de diferentes modos de natación, profundidad que suelen habitar y niveles tróficos. la morfometría de la aleta caudal (longitud, área y relación de aspecto), el índice hepatosomático y la relación entre músculo y esqueleto por unidad de longitud fueron determinados y comparados entre los individuos y entre especies a través de procedimientos estadísticos paramétricos y no paramétricos, multivariados y univariados. la variación intra-específica se relacionó con el tamaño y, para una única especie, también con el sexo. Se observaron dos patrones interespecíficos de variación: el primero fue interpretado como un gradiente de la capacidad de natación entre especies bentónicas y las más pelágicas, en función de la morfometría caudal y de las características corporales. el segundo se debió principalmente a la profundidad habitada y / o el nivel trófico. asociando los datos actuales a la información existente en la literatura, estas dos hipótesis se comprobaron y se examinaron en el contexto del tipo de natación del tiburón y el ambiente marino. a partir de las diferencias observadas en la morfometría de la aleta caudal, el hígado y las masas musculares, este documento ofrece por primera vez una base de datos cuantitativos y comparativos sobre los tiburones demersales, como gr...

Thermoregulation or Habitat Selection? Environmental Predictors of the Body Shape Variation in Sharks (Chondricthyes: Selachimorpha)

“…Despite not explicitly testing for phylogenetic autocorrelation, this study demonstrated that several phylogenetically distant orders -such as Hexanchiformes and Carcharhiniformes (Vélez-Zuazo & Agnarsson 2011) -present similar body shapes, while other more closely related orderssuch as Orectolobiformes and Squaliformes -have different body shapes. Therefore, the body shape of shark orders would not be a reflection of the evolutionary relationship between them, but rather an association with predation strategies and occupation of similar habitats, congruent with the idea that ecomorphological attributes tend to be related to locomotion (Cianciaruso et al 2009) and habitat occupation, as it has already been demonstrated for several shark species (Scacco et al 2010, Irschick & Hammerschlag 2015. These patterns described for sharks were contrasting with those reported to other marine mammals (cetaceans and pinnipeds), which exhibit results supporting the heat conservation hypothesis, but not habitat preference and availability hypotheses (Torres-Romero et al 2016).…”

“…This flattened body shape is common in species thriving in shallower and coastal regions (Kriwet et al 2010, Vaz & de Carvalho 2013 or in reef environments, where they await their prey in ambush strategies (Smith & Brown 2002, Baremore et al 2009, Raoult et al 2017. This type of morphology gives the species a slower and more manoeuvrable swim, typical of benthic species (Scacco et al 2010).…”

“…They compose a diverse group, representing one of the most speciose lineages of predators on the planet that play important functional roles in the top-down control of coastal and oceanic ecosystem structure and function (Compagno 1990, Ferretti et al 2010, Heithaus et al 2012. This successful evolutionary trajectory can be explainned by their sharp sensorial ability, reproductive strategies diversification, and great interspecific variability in body morphology, resulting in a great variety in the swimming mode and niche (feeding and habitat) among cartilaginous species (Camhi et al 1998, Scacco et al 2010, Irschick & Hammerschlag 2015. Selachimorpha species are the focus of multiple ecological, physiological and morphological studies (Garcia et al 2008, Vélez-Zuazo & Agnarsson 2011, Espinoza et al 2014, Irschick & Hammerschlag 2015, Davidson et al 2016.…”

You Are What You Eat, Microplastics in Porbeagle Sharks From the North East Atlantic: Method Development and Analysis in Spiral Valve Content and Tissue

“…To examine if the porbeagle shark's health was adversely affected by microplastic ingestion, we looked for a correlation between the average plastic particle per g w.w. in spiral valves content/tissue and several general health indices. In this case, the Hepatosomatic Index seemed to be the most relevant health indicator in relation to microplastic ingestion, maybe because it relates more directly to toxic effects (Scacco et al, 2010). Some microplastics will be excreted together with the rest of the spiral valve content.…”

Desarrollo del sistema motriz virtual de una plataforma subacuática móvil inspirada en biomimetismo

“…A pesar de que los mecanismos MPF usan sus aletas pares e impares para generar movimientos transitorios y/o nados periódicos, los BCF además de los nados periódicos también permiten una gran maniobrabilidad, y debido a su forma hidrodinámica el análisis cinemático es menos complejo que los MPF [5,7]. En la Figura 3 se presentan los modos de nado correspondientes a los BCF con sus direcciones de nado, en donde el modo anguiliforme es el que presenta un movimiento completamente ondulatorio [13] del cuerpo y el modo thunniforme un movimiento considerado como completamente oscilatorio [20]. De aquí que el ladeo sea mucho mayor en el modo anguiliforme.…”